[hldan]

I wanted to see what the main difference on cache speed between the 1.25Ghz iMacs w/7200RPM HD with the smaller 256k L2 and the G5 with the same HD but with larger the larger 512k L2 cache. I went to a local CompUSA and tested both machines. I noticed when photoshop is initially launched it equally takes the same time for both machines to start the program.
Upon quitting the program and starting them again they both launched photoshop much faster especially on the G5 but of course because the porgram has now been cached.

I also tried this same thing on a notebook Centrino PC with 1MB L2 Cache. It was very slow at initially launching photoshop but of course faster after the second launch.
So my question is, is the on chip L2 cache only for re-launching programs or does it serve other purposes for constant running programs?
Any help appreciated.

[KraziKid]

Originally posted by hldan:
I wanted to see what the main difference on cache speed between the 1.25Ghz iMacs w/7200RPM HD with the smaller 256k L2 and the G5 with the same HD but with larger the larger 512k L2 cache. I went to a local CompUSA and tested both machines. I noticed when photoshop is initially launched it equally takes the same time for both machines to start the program.
Upon quitting the program and starting them again they both launched photoshop much faster especially on the G5 but of course because the porgram has now been cached.

I also tried this same thing on a notebook Centrino PC with 1MB L2 Cache. It was very slow at initially launching photoshop but of course faster after the second launch.
So my question is, is the on chip L2 cache only for re-launching programs or does it serve other purposes for constant running programs?
Any help appreciated.

You cannot fairly compare those two macs because one is a G4, and the other is a G5. Also, the reason it loaded faster the second time around was because Windows and Mac OS X stored the temporary files used during launch in the temp folder. This allows you to open the program faster the second time around. You can think of the L2 cache as an extension to the system memory. Normal memory is behind the front side bus, which is a bottleneck for data transfer. The L2 cache lies on die (on the processor) and has no such bottleneck. The data stored in the L2 cache is data that is currently being used. The only reason that it loaded faster the second time around was because the operating system had made a cache of the files in a temporary folder so that it would not have to search for them again. Also, depending on the program, and how much you use it, the OS may decide to cache it in the system memory as well. I don't know if OS X does this, but I know that Windows will do this.

[hldan]

Thanks so much for clearing things up for me KraziKid. U R right it's an unfair comparison between the iMac and the G5 but I was just comparing them for the different cache sizes since they had the same HD.